1. Technical Field
The present invention relates to communication between a source apparatus and a destination apparatus, and in particular, to informing the destination apparatus of malfunctions (such as communication interruptions (or blackouts)) occurring in communication with the source apparatus.
2. Related Art
A conventional apparatus of this type is shown in Japanese Patent Application Publication (Laid-open) No. 2005-343183, in which two ECUs (electronic control units) are CAN-communicably connected to each other. One of the two ECUs is an EPS (electronic power steering)-ECU for controlling an electronic motor mounted in an on-vehicle steering gear box and the other is a steering-assist ECU which gives, as regular intervals, the EPS-ECU a control command showing a target steering torque under CAN communication protocol. Hence, in the publication, an amount of change in the in target steering torque is calculated and used to detect a malfunction in controlling lane keeping assist control. This control adopts a preset upper limit for limiting an amount of change between the current target torque and the last target torque. In addition, this publication teaches an increase in the preset upper limit when there occurs an interruption of communication between the steering assist ECU and EPS-ECU. This increase in the upper limit prevents the control command from being lost many times during the interruption.
In the system shown by the publication, in the similar way to other known systems, the EPS-ECU serves as a malfunction informing apparatus, which is able to store, in its nonvolatile memory, information showing “history of connection” with the source apparatus (steering assist ECU), once the EPS-ECU receives from steering assist ECU data showing the target steering torque. Since the data showing the connection history is stored in the nonvolatile memory, the malfunction informing apparatus is able to determine whether or not a duration during which the data have not been received from the source apparatus is over a preset period of time. That is, the communication interruption determination can be performed with the source apparatus. If it is determined that the duration is over the preset period of time, the EPS-ECU informs the fact that the communication with the source apparatus is interrupted. In contrast, if there is no connection history with the source apparatus in the memory, the malfunction informing apparatus estimates that this apparatus has not been connected the communication line, and it is not required to perform the communication interruption determination. Hence, in this case, this determination itself will not be performed.
However, when the determination itself will not be performed as above, the following drawbacks will be caused.
FIGS. 10A and 10B respectively show a communication system functionally including a malfunction reporting system. In the system shown in FIG. 10A, there is provided no ECU-A as shown in FIG. 10B. The ECU-A shown in FIG. 10A, which functions as a source apparatus, is a tire air-pressure monitoring apparatus in a vehicle, for example. In both FIGS. 10A and 10B, an ECU-B, which functions as a destination apparatus, is a meter ECU and connected to a display unit 50 through a direct line 80 to control the display unit 50. Through a communication line 70, this ECU-B is connected to another ECU which is designated as a malfunction informing apparatus, which is thus called “designated ECU”. A connection line 60 is connected to the designated ECU.
In the condition 1 in FIG. 10A where there is no ECU-A (source apparatus), there will be no communication between the designated ECU (malfunction informing apparatus) and the ECU-A, as a matter of course. In this case, information indicating “history of connection” with the ECU-A will not be written into the nonvolatile memory of the designated ECU, with the result that the memory maintains information indicating “no history of connection”.
As described, the designated ECU determines the communication interruption only in cases where information showing “history of connection” is written in its nonvolatile memory. Hence, in the condition 1 shown in FIG. 1, the designated ECU cannot detect that the ECU-A is unconnected to the communication line 60, and thus cannot inform the ECU-B of this unconnected state of the ECU-A with the communication line 60. This also prevents the ECU-B from informing users (for example, service persons of the vehicle) of this unconnected state through the display unit 50.
The condition 2 shown in FIG. 10B shows that at least one of the ECU-A and the communication line 60 is out of order and the communication therebetween cannot be performed. If this communication-disabled condition is caused at the beginning of incorporation of the ECU-A into a malfunction reporting system, the communication cannot be performed normally from the beginning between the ECU-A and the designated ECU. This results in that no information showing “history of connection” is written into the nonvolatile memory of the designated ECU, with no history of connection (history connection) kept therein.
In this condition 2, the designated ECU cannot detect a malfunction of either one or both of the ECU-A and the communication line 60 and an unconnected state of the ECU-A with the designated ECU due to the malfunction. The reason is that, as described before, the designated ECU can determine the communication interruption only when information showing “history of connection” is stored in its nonvolatile memory. As a result of this condition 2, the ECU-B cannot use the display unit 50 to report vehicle service persons of this malfunction.
In this way, the condition 1 exemplifies a malfunction of connection with the ECU-A, which is due to lack of the ECU-A which, under normal circumstances, should be incorporated in the malfunction reporting system. In contrast, the condition 2 exemplifies a malfunction of connection with the ECU-A due to a interruption caused at the ECU-A and/or the communication line 60, although the ECU-A exists in the malfunction reporting system. In any of the conditions 1 and 2, the designated ECU fails to detect and inform users of a malfunctioning state, contrary to the fact that a malfunction has occurred in the connection. This is cause there is stored no information showing “history of connection” in the nonvolatile memory of the designated ECU.
In addition, the conventional malfunction reporting system has another drawback. After information showing “history of connection” with the ECU-A is written into the nonvolatile memory of the designated ECU, the designated ECU may be replaced with new one due some reasons such as a malfunction occurring at the designated ECU itself. The new designated ECU has no information showing “history of connection” in its nonvolatile memory. In such a situation, the ECU-A and/or the communication line 60 may be out of order before the replacement. This results in the same condition as the foregoing condition 2. Hence, in this case, though there is actually a malfunction in the connection, it is impossible to inform the connection malfunction.